Main definitions of o in English

: O1O2O3


(also o)


  • 1The fifteenth letter of the alphabet.

    • ‘Little do you know, I used to be obsessed with a capital O.’
    • ‘For capital O, always form a C first, and then close it up.’
    • ‘Note the graceful shape of the o and s, and the fullness of the counters.’
    1. 1.1Denoting the next after N in a set of items, categories, etc.
      • ‘Susan Brown covers M, N, and O in her series that helps you to change your life at your own pace.’
    2. 1.2A human blood type (in the ABO system) lacking both the A and B antigens. In blood transfusion, a person with blood of this group is a potential universal donor.
      • ‘There are three alleles or versions of the blood type gene: A, B, and O.’
      • ‘Type Os don't find dairy products and grains quite as user friendly as do most of the other blood types.’
      • ‘The leading factor in weight gain for Type Os is the gluten found in wheat germ and whole wheat products, which interferes with insulin efficiency and slow down metabolic rate.’
  • 2Zero (in a sequence of numerals, especially when spoken)

  • 3A shape like that of a capital O; a circle.

    • ‘Pacing is especially troublesome - round shapes like "O" need less white space on either side than straight shapes like "H," of course, but there's also the question of how much white space the whole font needs.’
    • ‘Is there no way to rotate/ flip individual objects independently? e.g., when the O shape is brought into 3D it is in a vertical position.’

Main definitions of o in English

: O1O2O3


  • 1Ocean.

  • 2(in prescriptions) a pint.

  • 3Octavo.

  • 4October.

  • 5US Ohio.

  • 6Old.

  • 7Ontario.

  • 8Oregon.

  • The chemical element oxygen.

Main definitions of o in English

: O1O2O3



  • 1

    archaic spelling of oh
  • 2archaic Used before a name in direct address, as in prayers and poetry.

    ‘give peace in our time, O Lord’
    • ‘"Hear my prayer, O LORD, and give ear to my cry; Do not be silent at my tears; For I am a stranger with You, A sojourner like all my fathers."’
    • ‘O Lord, save thy people.’
    • ‘In the Church of England service for Evening Prayer we pray, “Give peace in our time, O Lord.”’


Natural exclamation: first recorded in Middle English.

Main definitions of o in English

: O1O2O3


  • 1Pint.

  • 2Octavo.

  • 3Off.

  • 4Old.

  • 5Only.

  • 6Order.

  • 7Baseball
    Out; outs.